Barometric relief air zone damper

ABSTRACT

A zone damper having a first portion controlled by a actuator to move between an open and a closed position in response to a zone thermostat, a second portion responsive to the static pressure in a HVAC system to open and bleed an amount of conditioned air past the damper when the static pressure of the system increases above a selected level, a coupling mechanism coupling the first and second portions to limit the relative movements of the two portions with respect to each other, and a biasing mechanism exerting a torque against the system static pressure differential.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/562,859 filed Jul. 31, 2012, which in turn is a continuation-in-partof U.S. Ser. No. 13/463,952 filed May 4, 2012, which claims the benefitof U.S. Provisional Patent Application Ser. No. 61/569,845 filed Dec.13, 2011, all of which are incorporated by reference.

BACKGROUND

This invention relates to heating, ventilating and air conditioning(“HVAC”) systems that include at least two zones controlled by sensors,generally thermostats, located within the at least two zones thatcontrol corresponding dampers in ducts leading from usually a singleHVAC source to the at least two zones.

In a conventional HAVC zoning system, conditioned air can be supplied toa plurality of zones, each zone being controlled by its own thermostat.Zoning systems for such an HVAC system typically includes zone dampersdisposed in the ductwork for controlling the air flow of the conditionedair to the zones in response to the thermostat. These zoning systemscontrol the flow of conditioned air to the plurality of zonesindependently so as to allow for independent control of the zoneenvironments. As a result, at any given time a number of zone dampersmay be open or closed. As the temperature in each zone is satisfied, itszone damper will close causing the static pressure in the duct system torise. This rise in static duct pressure can result in an increase innoise and drafts due, in part, to an increase in air flow velocitythough the ducts in zones still calling for conditioned air.

Conventionally, a bypass damper system is used to relieve excess staticduct pressure. For example, a bypass damper can be connected between thesupply and return air duct. If the bypass damper system determines thatthe air flow to a supply air duct is causing excess static ductpressure, then the bypass damper will be modulated open to recycle theconditioned air from the supply air duct to the return air duct. Thisimplementation has the disadvantage of being energy inefficient, andhence an expensive way to solve the problem. Bypass dampers can also beexpensive to install and difficult to setup. Elimination of theaforementioned bypass damper system could reduce the amount of HVACsystem equipment, which, in turn, would reduce installation andmaintenance costs.

What is needed is alternative apparatus that can effectively andefficiently control excess static duct pressure without resorting to theuse of a bypass damper.

SUMMARY

The alternative apparatus can take the form of each zone damper beingreplaced with a zone damper that, in addition to being controlled by thecorresponding zone thermostat, also includes a mechanical portionresponsive to the barometric pressure differential in the system to openand bleed a small amount of conditioned air into each zone when thestatic pressure of the system increases above a selected level.

In a preferred embodiment, the zone damper can include two portions thatare hinged to each other to permit independent movement of the twoportions relative to each other. A first of the portions can beconnected to a damper actuator controlled by a corresponding zonethermostat to open and close in response to the need for conditioned airwithin the zone. A second of the portions can also be moved by thedamper actuator from the closed position to an open position to ensuremaximum air flow through the duct in response to the need forconditioned air within the zone. As the first portion moves from theopen position to the closed position, the second portion can also movetoward the closed position, but may not entirely close if the staticpressure differential in the system is too high.

In a preferred embodiment, the second portion of the zone damper caninclude a counter balance weight, which may be adjustable, to set thedesired static pressure differential value that will be allowed. If thesystem static pressure differential rises above the set desired pressuredifferential value, the second portion responds by opening sufficientlyto reduce the system static pressure differential to the desired value.The counter balance weight and adjustment mechanisms can be of a varietyof constructions. A removable access panel can be provided in the zoneducting adjacent to the zone damper to permit access to and adjustmentof the counter balance weight to the desired level. Additionally, a lockor stop can be provided to fix the position of the second portionrelative to the first portion or to set the maximum deflection of thesecond portion relative to the first portion in certain situations.

In a further preferred embodiment, the zone damper can include acoupling mechanism between the damper blade and the damper actuator thatincludes a provision for limited relative movement so that the damperblade can respond to the barometric pressure differential in the systemto open and bleed an appropriate amount of conditioned air into eachzone when the static pressure of the system increases above a selectedlevel. The coupling mechanism can include a shaft coupled to one of thedamper blade and damper actuator and a cylinder surrounding the shaftcoupled to another of the damper blade and damper actuator, one of theshaft and cylinder including slot and the other of the shaft andcylinder including a projection into the slot defining limits to therelative movement between the shaft and cylinder. The shaft and cylinderneed not be of the same length.

A feature of the disclosed zone dampers is the inclusion ofbarometrically responsive portions that effectively eliminate the needfor any bypass damper system and hence reduce the size of damperinventory. An advantage of the disclosed zone dampers is a reduction indrafts and air noise, and a reduction in coil freeze up, with aresulting increase in system energy efficiency.

Other features and advantages of the present barometric zone damper andthe corresponding advantages of those features will become apparent fromthe following discussion of preferred embodiments, which is illustratedin the accompanying drawings. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of operation. Moreover, in the figures to the extentpossible, like referenced numerals designate corresponding partsthroughout the different views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a barometrically responsive zone damperpositioned within a shell.

FIG. 2 is a schematic side elevation view of a barometrically responsivezone damper positioned within a shell.

FIG. 3 is a schematic front elevation view of a barometricallyresponsive zone damper positioned within a shell.

FIG. 4 is a schematic front elevation view of another barometricallyresponsive zone damper positioned within a shell.

FIG. 5 is a schematic front elevation view of yet another barometricallyresponsive zone damper positioned within a shell.

FIG. 6 is a schematic front elevation view of still anotherbarometrically responsive zone damper positioned within a shell.

FIG. 7 is a side elevation view of a lock down clip that can be used ona barometrically responsive zone damper to control the relativedisplacement of the first and second portions of the damper with respectto each other.

FIG. 8 is a schematic sectional view of a barometrically responsive zonedamper moved to a partially open position by a damper actuator.

FIG. 9 is a schematic sectional view of a barometrically responsive zonedamper in a closed position with a lower portion being moved to apartially open position by virtue of a pressure differential across thedamper resulting in an air flow through the duct.

FIG. 10 is a schematic sectional view of a barometrically responsivezone damper that includes a coupling mechanism between the damper bladeand the damper actuator providing limited relative movement between thedamper blade and damper actuator.

FIG. 11 is a schematic sectional view of the barometrically responsivezone damper of FIG. 10 moved to a partially open position by a staticpressure differential across the damper resulting in an air flow.

FIG. 12 is a schematic sectional view of the barometrically responsivezone damper of FIG. 10 moved to a fully open position by the damperactuator.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a barometrically responsive zone damper 10 positionedwithin a segment of ducting 11, which forms a damper shell 12. Thedamper 10 can include an upper portion 14 and a lower portion 16. Theupper portion 14 can be fixed to a shaft 18 mounted in bushings fixed inthe shell 12, the shaft 18 extending through the shell 12. The positionof the shaft 18 and upper portion 14 of the zone damper 10 can becontrolled by a damper actuator 22 that can be located on the outside orinside of the shell 12. The damper actuator 22 can be situated on eitherside of the shell 12 and controlled by a zone thermostat, not shown. Thelower portion 16 of the zone damper 10 is connected to the upper portion14 of the damper by a hinge 24 to permit independent movement of thelower portion 16 relative to the upper portion 14. In the absence of asufficient air pressure differential or air flow through the ducting 11,the force of gravity will cause the lower portion 16 to pivot to aposition in alignment with the upper portion 14 as shown. The forceacting to close the lower portion 16 can be increased by attaching aweight 26 of selected size to the lower portion 16.

The amount of the force acting to close the lower portion 16 can bemodified by modifying the size of the weight 26 or by adjusting theposition the weight 26 so as to increase or decrease the torque appliedto the lower portion 16 as shown in FIG. 1 and FIG. 3. A removableaccess panel 25 can be provided in the shell 12 adjacent to the zonedamper 10 to permit access to and adjustment of the counter balanceweight 26 to the desired level. FIG. 3 also shows the upper portion 14fixed to the shaft 18, which can be mounted in bushings 20, which can beformed of nylon or similar durable material, fixed in the shell 12, theshaft 18 extending through the shell 12. Both portions 14 and 16 areshown to have a gasket 15, 17 adjacent to the shell 12 to provide asuitable seal to prevent unwanted leaking past the zone damper 10. Alock 34 can also be provided to fix the position of the lower portion 16in relation to the upper portion 14. The lock 34 can take the form of abutterfly blade lock 36. When barometric pressure differential relief isdesired, the butterfly blade lock 36 can be rotated from the lockedposition shown in FIG. 1 to a horizontal un-locked position as shown inFIG. 4.

A variations of the barometric zone damper is shown in FIG. 2, which isa schematic side elevation view of a barometrically responsive zonedamper 10 positioned within a shell 12. The damper 10 is shown toinclude an upper portion 14 and a lower portion 16. The position of theupper portion 14 of the zone damper 10 can be controlled by a damperactuator 22 that can be located on the outside of the shell 12. Thedamper actuator 22 can be controlled by a zone thermostat, not shown.The lower portion 16 of the zone damper 10 is connected to the upperportion 14 in a manner to permit independent movement of the lowerportion 16 relative to the upper portion 14. In the absence of asufficient air pressure differential on opposite sides of the zonedamper 10, or any air flow through the ducting 11, the force of gravitywill cause the lower portion 16 to pivot into alignment with the upperportion 14. Gaskets 27 can be included in the shell 12 to seal againstdamper portions 14 and 16 when the portions are in a closed position.One or more weights 26 can be added to or subtracted from a screw 28located adjacent to a lower margin 30 of the lower portion 16 toincrease or decrease the force acting to close the lower portion 16.

FIG. 4 shows a schematic front elevation view of another barometricallyresponsive zone damper 10 positioned within a shell 12. The damper 10 isshown to include an upper portion 14 and a lower portion 16. Theposition of the upper portion 14 of the zone damper 10 can be controlledby a damper actuator 22 located on the outside of the shell 12. Thelower portion 16 is connected to the upper portion 14 in a manner topermit independent movement of the lower portion 16 relative to theupper portion 14. In the absence of a sufficient air pressuredifferential on opposite sides of the zone damper 10, or any air flowthrough the shell 12, the force of gravity will cause the lower portion16 to pivot into alignment with the upper portion 14. A lock 34 can alsobe provided to fix the position of the lower portion 16 in relation tothe upper portion 14. The lock 34 can take the form of a butterfly bladelock 36. If, in a particular installation, no barometric pressuredifferential relief is deemed necessary, the butterfly blade lock 36 canbe rotated from the un-locked position shown in FIG. 4 to a verticallocked position, in which case the damper 10 would perform as aconventional zone control damper.

FIG. 5 is a schematic front elevation view of yet another barometricallyresponsive zone damper 10 positioned within a shell 12. The damper 10 isshown to include an upper portion 14 and a lower portion 16. Theposition of the upper portion 14 of the zone damper 10 can be controlledby a damper actuator 22 located on the outside of the shell 12. It is tobe noted that in this embodiment, no counter balance weight is coupledto portion 16. Instead, the portion 16 is connected to the portion 14 byspring biased hinges 23, each incorporating a helical torsion spring 54,the hinges permitting independent movement of the portion 16 relative tothe portion 14 and the springs 54 providing a desired biasing force. Inthe absence of a sufficient air pressure differential on opposite sidesof the zone damper 10, or any air flow through the shell 12, the forceprovided by the spring biased hinges 23 will cause the lower portion 16to pivot into alignment with the upper portion 14. The amount of forcecan be determined by specifying the strength of the spring element 54included in the spring biased hinges 23, or by specifying the number ofspring biased hinges coupling the upper portion 14 to the lower portion16. While the spring element 54 providing the biasing force has beenillustrated as being incorporated into a spring biased hinge 23, thespring can take other forms including, for example, a leaf or bowspring, or a volute spring, coupled to both the upper portion 14 and thelower portion 16. The shaft 18 can be located at any angle relative toHVAC system as a whole, since the position of portion 16 in relation toportion 14 is not governed entirely by gravity, but rather by the forcesupplied by the one or more springs. This allows for the barometricallyresponsive zone damper 10 to be located in a duct 12 that may bevertically oriented or at least inclined so that the force opposing anypressure differential is only partly dependent on gravity.

A lock 34 can also be provided to fix the position of the lower portion16 in relation to the upper portion 14. The lock 34 in FIG. 5 takes theform of a strap 38, which can include a series of holes 40 or a slotpermitting the strap to be adjusted from an unlocked position as shownin FIG. 5 to a position where a lower end 42 of the strap 38 overlaps atleast a portion of lower portion 16 to maintain the upper portion 14 andlower portion 16 in alignment with each other. When the strap 38 is inthe locked position, the damper 10 would perform as a conventional zonecontrol damper.

FIG. 6 is a schematic front elevation view of still anotherbarometrically responsive zone damper 10 positioned within a shell 12,which is shown to be rectangular. The shape of the perimeter of the zonedamper 10 can be formed in any shape necessary for a given installation.Again, damper 10 is shown to include an upper portion 14 and a lowerportion 16. The position of the upper portion 14 of the zone damper 10can be controlled by a damper actuator. FIG. 6 shows a damper actuator22 that has a sufficiently low profile to lie in the region of a damperframe 47 surrounding the shell 12, and between the shell 12 and a dampermounting plate 49 supporting the damper 10 in the related HVAC system.As in the other embodiments, the lower portion 16 is connected to theupper portion 14 by hinges 24 to permit independent movement of thelower portion 16 relative to the upper portion 14. In the absence of asufficient air pressure differential on opposite sides of the zonedamper 10, or any air flow through the shell 12, the force of gravitywill cause the lower portion 16 to pivot into alignment with the upperportion 14. A lock 34 can also be provided to fix the position of thelower portion 16 in relation to the upper portion 14. The lock 34 inFIG. 5 takes the form of a strap 38, which includes a slot 44 permittingthe strap to be adjusted from an unlocked position as shown in FIG. 6 toa position where a lower end 42 of the strap 38 overlaps at least aportion of lower portion 16 to maintain the upper portion 14 and lowerportion 16 in alignment with each other. When the strap 38 is in thelocked position, the damper 10 would perform as a conventional zonecontrol damper.

The strap 38 can also take the form shown in FIG. 7 is a side elevationview of a clip 46 that includes a first portion 48 that can be coupledto a surface of the upper damper portion 14. The clip 46 can alsoinclude a second portion 50 that can be inclined at an angle a withrespect to portion 48. The clip first portion 48 can be positioned onthe upper damper portion 14 so that the junction 52 of the portions 48and 50 overlies the junction of the upper damper portion 14 and thelower damper portion 16. The angle a of the clip 46 sets a maximumdeflection that the second portion 16 of the damper 10 can achieverelative to the first portion 14. While FIG. 7 shows the portions 48 and50 of clip 46 to be inclined at an angle of about 110° relative to eachother, the angle can range between about 90° and 140°. While FIG. 7shows the length L₁ of portion 48 to be greater than the length L₂ ofportion 50, the portions 48 and 50 may be of equal length.

An appreciation of the operation of the barometrically responsive zonedampers 10 can be gained from a consideration of FIGS. 8 and 9 in whichthe damper 10 includes a first portion 14 and a second portion 16. Thefirst portion 14 is fixed to shaft 18 so that any rotation of shaft 18will cause a corresponding angular displacement of the portion 14. Theposition of the shaft 18 and first portion 14 of the zone damper 10 canbe controlled by a damper actuator 22 that can be, in turn, controlledby a zone thermostat, not shown. The second portion 16 is connected byone or more hinges to the first portion 14 to permit independentmovement of the second portion 16 relative to the first portion 14. Abiasing force supplied by one or more weights, springs, or other biasingmeans, or a locking element can be suitably positioned, to maintain thesecond portion 16 in alignment with the first portion 14 as shown inFIG. 8. As the shaft 18 rotates from a closed position C, in which thedamper 10 blocks air flow through the duct 12, to a partially openposition O, in which air can flow through the duct 12 past the damper10, both portions 14 and 16 move with the rotation of the shaft 18 inthe manner of a conventional zone control damper.

In the absence of a locking element, or with the locking elementsituated in an un-locked position allowing relative movement betweensecond portion 16 and first portion 14, the rotation of shaft 18 willstill cause a corresponding angular displacement of the portion 14.Portion 16, however, is free to respond to a pressure differentialacross the damper 10, which if sufficient to overcome the biasing force,will allow portion 16 to open to a relief position R even though portion14 remains in the closed position C as shown in FIG. 9 to bleed asufficient amount of air through the duct 12 to keep the static pressuredifferential from rising to an unacceptable level.

With each of the illustrated variations, if the system static pressuredifferential rises above the set desired pressure value, the lower orsecond portion 16 of the zone damper 10 can respond by openingsufficiently to reduce the system static pressure to a desired value. Ina preferred system, the biasing force supplied by the one or moresprings, or by the weights 26, can be such that the second or lowerportion 16 of the damper 10 will begin to open independent of the firstportion 14 at approximately 0.3″ WC of static pressure. The use of anyof the illustrated variations of barometric zone dampers effectivelyeliminates the need for any bypass damper system.

FIGS. 10-12 show the operation of a zone damper 10 of a slightlydifferent design that includes a shell 12 containing a damper blade 14coupled to a shaft 18. The damper blade 14 can be in the form of a onepiece, un-divided blade. A cylinder 56 can surround at least a portionof the shaft 18, the cylinder 56 being controlled by an actuator 22. Theshaft 18 is shown to include a slot 58, while the cylinder 56 is shownto include a projection 60 that projects into the slot 58. The cylinder56 is movable by the actuator 22 between a closed position shown in FIG.10, and an open position shown in FIG. 12 in response to a suitablethermostat, not shown. The damper blade 14 and shaft 18 are movablerelative to the cylinder 56 in response to the static pressuredifferential in an HVAC system as shown, for example in FIG. 11, tobleed an amount of conditioned air past the damper blade 14 when thestatic pressure differential of the system increases above a selectedlevel. The end 62 and end 64 of slot 58, shown in FIG. 11, define thelimits of travel of the projection 60 within the slot 58 and thecorresponding limits of travel of the shaft 18 within the cylinder 56.As in the prior embodiments, the force acting to close the damper blade14 can be increased by attaching a weight 26 of selected size to asuitable location on the damper blade. The amount of the force acting toclose the damper blade 14 can be modified by modifying the size of theweight 26 or by adjusting the position the weight 26 so as to increaseor decrease the torque applied to the damper blade.

It will be appreciated by those skilled in the art that the shaft 18could be coupled to the actuator 22, while the cylinder 56 could becoupled to the damper blade 14. It will also be appreciated by thoseskilled in the art that the slot 58 could be located on the interiorsurface of the cylinder 56, while the projection 60 could projectoutward from the shaft 18 into the slot. The shaft 18 and cylinder 56need not be of the same length. While the slot 58 is shown to providefor about 90° of relative movement between the shaft and cylinder, thescope of relative movement is subject to some choice of design and maybe limited or enlarged to provide less or more relative movement. Itwill also be appreciated by those skilled in the art that a suitablespring could be substituted for the weight 26 to provide the desiredbiasing force, the spring being coupled, for example, between the shaft18 and the cylinder 56.

While these features have been disclosed in connection with theillustrated preferred embodiments, other embodiments of the inventionwill be apparent to those skilled in the art that come within the spiritof the invention as defined in the following claims.

1. A method of operating a zone damper comprising: activating anactuator to position a mechanical blade portion of the zone damper in afirst position to substantially inhibit a flow of conditioned airthrough a shell of the zone damper, the position of the mechanical bladeportion in the first position responsive to a signal; enabling movementof the mechanical blade portion in a predetermined range while in thefirst position, the movement of the mechanical blade portion responsiveto a static pressure differential, so that the static pressuredifferential increasing above a selected level causes movement of themechanical blade portion to bleed an amount of conditioned air past themechanical blade portion; and activating the actuator to drive themechanical blade portion to a second position, responsive to the signal,to allow a maximum flow of conditioned air through the shell of the zonedamper, wherein the mechanical blade portion is not responsive to thestatic pressure differential while in the second position.
 2. The methodof claim 1, further comprising: activating the actuator to drive themechanical blade portion to a third position to partially block the flowof conditioned air through the shell of the zone damper responsive tothe thermostat signal; and enabling movement of the mechanical bladeportion in a second predetermined range while in the third position,responsive to the static pressure differential increasing above a secondselected level to allow a variable amount of conditioned air past themechanical blade portion, the variable amount of conditioned air whilethe mechanical blade portion is in the third position being greater involume than the amount of conditioned air while the mechanical bladeportion is in the first position.
 3. The method of claim 2, wherein thepredetermined range of the mechanical blade portion in the firstposition is greater than the second predetermined range of themechanical blade portion in the third position.
 4. The method of claim2, wherein the third position is between the first position and thesecond position.
 5. The method of claim 1, further comprising biasingthe movement of the mechanical blade portion to a first end of thepredetermined range by a biasing member.
 6. The method of claim 1,wherein the movement of the mechanical blade portion is caused by thestatic pressure differential.
 7. The method of claim 1, wherein themechanical blade portion is coupled to the actuator by a shaft whichpasses through the shell of the zone damper.
 8. The method of claim 7,wherein movement of the mechanical blade portion is limited to thepredetermined range by the movement of a projection within a slot,wherein one of the projection or the slot is associated with themechanical blade portion and the other of the projection or the slot isassociated the shaft.
 9. The method of claim 1, further comprisingproviding the amount of conditioned air to a zone.
 10. A method ofoperating a zone damper comprising: activating an actuator to drive ashaft to a first position responsive to a temperature signal, whereinthe shaft is coupled to a mechanical blade portion of the zone damper;enabling movement of the mechanical blade portion toward a first end ofa predetermined range about the shaft so that the mechanical bladeportion is substantially blocking a flow of conditioned air through ashell of the zone damper, while the shaft is in the first position,enabling variation in positioning of the mechanical blade portion withinthe predetermined range by a static pressure differential so that thestatic pressure differential increasing above a selected level moves themechanical blade portion to allow an amount of conditioned air to bleedpast the mechanical blade portion towards a zone; and activating theactuator to drive the shaft to a second position responsive to thetemperature signal, to allow a substantially unrestricted flow ofconditioned air through the shell of the zone damper towards a zone,wherein the mechanical blade portion is not responsive to the staticpressure differential while the shaft is in the second position.
 11. Themethod of claim 10, further comprising: activating the actuator to drivethe shaft to a third position, responsive to a temperature signal; whilethe shaft is in the third position, enabling movement of the mechanicalblade portion toward the first end of the predetermined range about theshaft, so that the mechanical blade portion partially blocks the flow ofconditioned air through the shell of the zone damper; and enablingvariable movement of the mechanical blade portion in the predeterminedrange while in the third position, by a static pressure differentialincreasing above a second selected level or decreasing below the secondselected level to allow a variable amount of conditioned air past themechanical blade portion towards a zone, the variable amount ofconditioned air while the shaft is in the third position being great involume than the amount of conditioned air while the shaft is in thefirst position.
 12. The method of claim 11, wherein the predeterminedrange of the movement of the mechanical blade portion while the shaft isin the first position is greater than the predetermined range ofmovement of the mechanical blade portion when the shaft is in the thirdposition.
 13. The method of claim 11, wherein the third position isbetween the first position and the second position.
 14. The method ofclaim 10, further comprising biasing the movement of the mechanicalblade portion to a first end of the predetermined range by a biasingmember.
 15. A method of operating a zone damper comprising: activatingan actuator, responsive to a thermostat signal, to drive a shaft of thezone damper to a first position, the first position having a first endelement, wherein the shaft is coupled to a mechanical blade portion ofthe zone damper, and wherein the first end element defines a limit as toa range of motion of the mechanical blade portion with respect to thefirst end element; while the shaft is in the first position, enablingmovement of the mechanical blade portion to substantially block a flowof conditioned air through a shell of the zone damper; while the shaftis in the first position, enabling variable movement of the mechanicalblade portion in the range of motion, the variable movement of themechanical blade portion responsive to a static pressure differential,so that the static pressure differential increasing above a selectedlevel causes movement of the mechanical blade portion to bleed an amountof conditioned air past the mechanical blade portion; and activating theactuator, responsive to the thermostat signal, to drive the shaft to asecond position to allow the flow of conditioned air through the shellof the zone damper, wherein the while the shaft is in the secondposition, the mechanical blade portion is not responsive to the staticpressure differential.
 16. The method of claim 15, wherein the range ofmotion is defined between the location of the first end element, and apoint wherein the mechanical blade portion is not responsive to thestatic pressure differential.
 17. The method of claim 16, furthercomprising: activating the actuator to drive the shaft to a thirdposition, responsive to a thermostat signal, wherein the mechanicalblade portion rests against the first end element and is positioned topartially block the flow of conditioned air through the shell of thezone damper; and while the shaft is in the third position, enablingvariable movement of the mechanical blade portion in the range of motionwhile in the third position, responsive to the static pressuredifferential increasing above a second selected level to allow avariable amount of conditioned air past the mechanical blade portion,the variable amount of conditioned air while the shaft is in the thirdposition being great in volume than the amount of conditioned air whilethe shaft is in the first position.
 18. The method of claim 16, whereinthe first end element is located at a first end of a slot, and whereinvariable movement of the mechanical blade portion is limited by themovement of a projection within the slot.
 19. The method of claim 18,further comprising enabling variable movement of the mechanical bladeportion against a second end of the slot to define a maximumresponsiveness of the mechanical blade portion to move in the range ofmotion in response to the static pressure differential.
 20. The methodof claim 15, further comprising biasing the movement of the mechanicalblade portion to a first end of the range of motion by a biasing member.